I guess I'll be the one person here who reviews this item and actually knows something about Airsoft.
For me, last time it was chrono'd at the field, it did 415 fps w/ 0.2s, so that means I'm getting more FPS than I should because of the great compression this gearbox gives and the fact that I'm using a Madbull 6.03mm tightbore barrel.

The only 2 problems is that the AIM gears are Infinite Torque-Up, so the ROF is going to be a tad slow because of the gear ratio of the gears. I'm running mine with an AMP T5000L High Torque motor which gave me 25 rps on Standard ratio gears, and gives me 16 rps on these gears. Also the gears sound really whiny, and is hard to adjust the motor height because of the way the gears sound.

The Advantage is that, the trigger response is tremendous.

The other problem is that the piston head is really shitty, and mine destroyed itself and got caught in the cylinder head locking the compression parts, making it sound like the piston itself was stripped after 10,000 rounds. However, I changed that, and now it's still great.

I'm really happy with this gearbox, and it is very much worth the pricetag. If I made another custom M4, this would be the gearbox I use.

ALSO!! A word of precaution, before I forget. The wiring out the gearbox for the battery is a small tamiya, I'm using a 9.6v 4200 mah Powerizer battery which is gigantic, but can squeeze into an M16 stock, but I did it by running a couple long connectors over the top of the battery, so that the two connectors are near the door to the stock for easy connecting and disconnecting, and also I did this way so I can leave the battery in the stock when charging it.

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